The overall objective of the research program in this laboratory is the description of events during the initial phases of mammalian embryogenesis in cellular and molecular terms. During the proposed project period, the research will be concerned primarily with two aspects of preimplantation embryogenesis: (1) A definition of the role of gene products synthesized during oogenesis in the developmental program which follows fertilization; and (2) A definition of the major and significant interactions between the uterine stage embryo and the maternal reproductive tract which permit the completion of events leading up to implantation. Previous work in this laboratory has provided a background description of gene expression during the preimplantation period of rabbit embryogenesis, in terms both of ribonucleic acid and of protein synthesis. It is anticipated that this description will require refining as work progresses during the proposed project period. Current evidence is consistent with the hypothesis that gene products synthesized during mammalian oogenesis are stable and do indeed participate in the protein synthetic events which follow fertilization. However, the relative importance of these products with respect to those synthesized following fertilization is not known. Likewise, the molecular basis of the requirement for synchrony between developing preimplanted embryo and reproductive tract is not understood, nor is the mechanism by which the reproductive tract may reversibly arrest embryonic cell division. These questions will be explored using the techniques of in vitro egg fertilization, cell-free protein synthesis, two-dimensional polyacrylamide gel electrophoresis, electron microscopy, and autoradiography. In addition, chemical analyses of the ionic composition of reproductive tract secretions during early gestation in both the rabbit and mouse are anticipated, along with the effect of macromolecules in these secretions on ion uptake by the embryo.